The White House has confirmed that the terror attack that killed four Americans at the Libya consulate was orchestrated by al-Qaida sympathizers, but questions remain about when it was planned. NBC's Andrea Mitchell reports.

The siege of the U.S. consulate in Benghazi, Libya last week that left four dead, including Ambassador Chris Stevens, was a "terrorist attack," a White House spokesman said Thursday.

Since the Benghazi attack occurred amid protests of an American-made anti-Islam video that was circulating on the Internet, it has been unclear whether it was planned independently or launched opportunistically when the demonstration was under way, or if it was a spontaneous attack emerging out of the protests.

This was the first time the White House called it a "terrorist attack."

Esam Omran Al-fetori / Reuters file

An armed man reacts as the U.S. Consulate in Benghazi burns on Sept. 11 after protests purportedly sparked by an anti-Islam film by a U.S. filmmaker.

"We are looking at indications that individuals involved in the attack may have had connections to al-Qaida or al-Qaida affiliates," said Carney, who noted that the FBI is investigating.

"According to the best info we have right now it was an opportunistic attack on our mission in Benghazi."

The low-budget video, "Innocence of Muslims," with its insulting portrayal of Islam’s prophet Muhammad, had been circulating on the Internet for months, and it is unclear why it became a focal point of anger in the Muslim world just before the anniversary of the 9-11 attacks on the United States.

White House Press Secretary Jay Carney speaks during his daily news briefing at the White House on Wednesday.

"What we do know is that the natural protests that emerged over the video were used as an excuse by extremists," said President Barack Obama, speaking at a forum hosted by the Spanish-language TV station Univision on Thursday about the attacks on diplomatic posts in Libya and Egypt.

Protests, some of them violent, have erupted at U.S. diplomatic missions across majority Muslim countries in the Middle East, Africa and Asia in the past week.

In Benghazi, the attack on the consulate took the lives of Stevens, as well as information management officer Sean Smith and security personnel Tyrone Woods and Glen Doherty, all of whom were honored in a ceremony at Andrews Air Force Base last week as their remains were returned to the United States.

Amid questioning from U.S. legislators about the security at the U.S. outpost in Libya, Secretary of State Hillary Clinton on Thursday announced that she is forming an accountability review board to look at the attack on the Benghazi consulate. The board will be led by retired Ambassador Thomas Pickering, she told reporters at a press conference.

Clinton said she was scheduled to brief senators and congressmen on Benghazi later Thursday. She said she expected the briefing would cover the security posture at the post before, during and after the attack, and the steps the government has taken since to protect U.S. personnel worldwide.

"I will also talk about the importance of the broader relationship with these countries in light of the events of the past days," Clinton said. "There are obviously very real challenges in these new democracies, these fragile societies."

Clinton said she will be joined on the Hill by Director of National Intelligence James Clapper, Deputy Secretary of Defense Ash Carter, Vice Chairman of the Joint Chiefs of Staff Sandy Winnefeld, and experts from FBI, the State Department, and elsewhere in the government.

Clinton was asked about a report that alleges Stevens told others that he was on an al-Qaida hit list. She said she has no information or reason to believe there is any basis for that.